1. Field of the Invention
The present invention relates to a semiconductor device and a temperature change detecting device. More particularly, the present invention relates to a semiconductor device including a processing circuit which needs temperature compensation to provide intended functions properly, and to a temperature change detecting device which detects changes in the temperature of an object of interest.
2. Description of the Related Art
It is known that the characteristics of electronic circuit components formed on a semiconductor substrate have some temperature dependence. On-chip resistors, for example, show variations in the resistance when the temperature changes. For this reason, the cutoff frequency of an active filter implemented on a semiconductor chip would vary with the substrate temperature if its temperature-sensitive elements were not corrected appropriately.
Researchers have proposed various temperature compensation methods to address the above problem. FIG. 10 shows a conventional compensation circuit where one such method is implemented. The illustrated circuit is composed of a first constant current source 10, an internal component 11, a second constant current source 12, an external component 13, a voltage difference detector 14, and a circuit 15 that needs temperature correction. These circuit elements are formed on a semiconductor device, except for the external component 13.
The first constant current source 10 supplies the internal component 11 with a constant current. The internal component 11 is, for example, a resistive element formed as part of the semiconductor device. The second constant current source 12 supplies the external component 13 with a constant current. The external component 13 is another resistive element placed outside of the semiconductor device so as not to be affected by the temperature of the device.
The voltage difference detector 14 senses the voltage difference between the internal component 11 and external component 13 and creates a n-bit signal representing that difference. This signal is supplied to the circuit 15 (e.g., active filter) which needs temperature compensation.
The circuit of FIG. 10 operates as follows. Upon power up, the first and second constant current sources 10 and 12 begin to supply a constant current to their respective load circuits 11 and 13, the former being located inside the device and the latter being located outside the device. Consider, for example, that the constant current sources 10 and 12, internal components 11, and external component 13 are designed to produce zero volts as a voltage difference between the upper nodes of the internal component 11 and external component 13 at room temperature (25 degrees Celsius). Since this condition holds during a certain period immediately after the device is powered up, the voltage difference detector 14 supplies the circuit 15 with a n-bit signal indicating that no voltage difference is detected. With this n-bit signal, the circuit 15 applies a prescribed signal processing function (e.g., filtering) to the given input signal with its default circuit parameters.
Suppose that a certain time has passed and the temperature of the semiconductor device has risen. While the temperature of the internal component 11 rises accordingly, the external component 13 located outside the semiconductor device stays at the same temperature. If the internal component 11 and external component 13 have a positive temperature coefficient (i.e., their resistances go up with temperature), the internal component 11 will exhibit a larger resistance than the external component 13. This means that the voltage developed across the internal component 11 will be greater than that of the external component 13 (assuming that the two constant current sources 10 and 12 output the same amount of current).
The voltage difference detector 14 now detects a non-zero voltage difference between the internal component 11 and external component 13 and creates a n-bit signal representing that difference for delivery to the circuit 15. Suppose that the voltage drop of the internal component 11 is 5.2 volts while that of the external component 13 is 5.1 volts. The voltage difference detector 14 then notifies the circuit 15 of the voltage difference by sending an n-bit signal representing that value, 0.1 volts.
The circuit 15 corrects itself with reference to the n-bit signal received from the voltage difference detector 14. Since it is 0.1 volts in the present example, the circuit 15 controls an integral resistive element in such a way that its resistance will be reduced to cancel out the temperature-induced increase. By doing so, the circuit 15 can maintain its own operating characteristics even if the device temperature is increased.
The conventional configuration explained above in FIG. 10, however, needs a mounting space for the external component 13 other than the semiconductor device itself. This is a disadvantage under some circumstances where the space limitation is tight. Another problem of the conventional circuit is that the output current of the constant current sources 10 and 12 may change with temperature because of the temperature dependence of circuit components used in them. This means that a measurement error would be introduced to the detected difference voltage.
Referring next to FIG. 11, another example of a conventional temperature compensation method will be shown. The illustrated circuitry comprises a circuit 20, a subtractor and integrator 21, an evaluation circuit 22, a resistance controller 23, and a clock generator 24.
The circuit 20 is an active filter composed of resistors, capacitors, integrators, and other elements. The subtractor and integrator 21 integrates the voltage developed across one of the resistors in the circuit 20. It subtracts a DC offset from that voltage, if any, so as not to include such an offset in the result of integration.
The evaluation circuit 22 compares the output of the subtractor and integrator 21 with a predetermined reference signal and passes the result to the resistance controller 23. According to the comparison result, the resistance controller 23 controls the value of a certain resistive element that governs the characteristics of the circuit 20. The clock generator 24 provides the subtractor and integrator 21 and evaluation circuit 22 with a clock signal since they use switched-capacitor techniques.
The circuit of FIG. 11 operates as follows. When the semiconductor device is powered up, the circuit 20 starts to operate as an active filter. Timed with respect to the clock signal supplied from the clock generator 24, the subtractor and integrator 21 integrates the voltage developed across a particular resistor in the circuit 20 and sends the result to the evaluation circuit 22. The integration result contains no DC offset component of the voltage of interest because the subtractor and integrator 21 rejects it before integration.
The evaluation circuit 22 compares the output signal of the subtractor and integrator 21 with a predetermined reference signal and passes the result to the resistance controller 23. Suppose, for example, that these two signals agree with each other at room temperature (25 degrees Celsius). The evaluation circuit 22 then notifies the resistance controller 23 of the agreement between the two signals since the device temperature is almost the same as the ambient temperature just after power-up. While it is designed to modify the value of a certain resistive element in the circuit 20 according to the comparison result, the resistance controller 23 does nothing to the circuit 20 at the moment since the difference value has been observed to be zero.
As the time has passed after power-up, the temperature of the resistive element of interest goes up with the device temperature, causing a variation of the circuit parameter (i.e., resistance). This variation can be observed at the output of the subtractor and integrator 21. By comparing the output signal with a predetermined reference signal, the evaluation circuit 22 detects the variation and so notifies the resistance controller 23. The resistance controller 23 interprets it as a change in the resistance parameter in the circuit 20, thus modifying the internal setup of the circuit 20 to compensate for the variation. In the case the resistive element of interest has a positive temperature coefficient (i.e., the resistance increases as the temperature rises), the resistance controller 23 takes an action to reduce the resistance to compensate for the temperature increase. Through the above processing, the operating characteristics of its internal circuit 20 can be maintained even if the device temperature is increased.
The above-described conventional circuit of FIG. 11, however, exhibits some temperature dependence at one of its circuit blocks that produces the reference signal. This means that the reference signal may vary as the temperature changes, thus introducing an error to the temperature measurement.
In view of the foregoing, it is an object of the present invention to provide a semiconductor device with a temperature compensation circuit which detects temperature changes accurately, without requiring extra mounting space.
It is also an object of the present invention to provide a temperature change detecting device which detects temperature changes accurately, without requiring extra mounting space.
To accomplish the first object stated above, the present invention provides a semiconductor device comprising the elements that operate as follows. A processing circuit performs a predetermined function, which has some temperature dependence. A sensor unit is located in the vicinity of the processing circuit, which comprises a first and second semiconductor components having different temperature coefficients from each other. A temperature change detector detects a temperature change by observing a change in a certain property of the first and second semiconductor components constituting the sensor unit. A temperature corrector modifies a circuit parameter of the processing circuit to compensate for the temperature change detected by the temperature change detector.
To accomplish the second object stated above, the present invention provides a temperature change detecting device which detects changes in the temperature of an object of interest. This device comprises a sensor unit located in the vicinity of the object of interest, which comprises a first and second semiconductor components having different temperature coefficients from each other. A temperature change detector detects a temperature change by observing a change in a certain property of the first and second semiconductor components constituting the sensor unit.
The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.